Field of the Invention
This invention relates generally to the field of exploration and production for hydrocarbons. More specifically, the invention relates to a method of using active or passive seismic signals transmitted along a well casing to determine the structural integrity of the well casing.
Background of the Invention
A well for producing hydrocarbons generally includes a casing cemented to the wellbore which penetrates the formation and one or more injection or production tubes within the casing. Occasionally, an open bore hole, i.e., one without a casing, contains the injection or production tubing strings therein. The well may often penetrate numerous production or injection zones of interest. Casing or tubing impairment or damage may lead to loss of pressure integrity, pinching of production tubing, or an inability to lower tools into the well. Damage or impairment to the casing and/or tubing may occur through shear owing to displacement of the rock strata along bedding planes or along more steeply inclined fault planes, also known as shear failures. These failures may be triggered by stress concentrations generated by changes in volume resulting from production or injection activity from a hydrocarbon producing reservoir. The volume changes may come about from pressure changes, temperature changes, or solids movement (solids/liquids injection or production).
There are various mechanisms for casing damage which are recognized, including compression, tension, corrosion and shear. Compressional failures may occur within a producing interval due to large vertical strains associated with compaction. Tensile failures can result when material outside of the compacting zone provides vertical support to material above the compacting zone. Thermal expansion due to steam injection may also contribute to development of tensile stresses in an overburden. Corrosion can occur because of a presence of chemically active fluids in rock. Shear failures may also be induced by horizontal displacements along weak bedding planes or reactivated faults in the overburden above a reservoir. Once well shear or well damage is detected, appropriate corrective actions may be taken to avoid and prevent any incidents from occurring. Consequently, there is a need for methods and systems for detecting well shear failures.